it in this half hour, that high-stakes trial here in new york a swimsuit designer found dead in the bathtub of her swanky hotel room. Her boyfriend a privileged show background now on trial for her murder. Amy, you've been following this. Friends of 33-year-old sylvie cache said she was trying to break off the relationship with brooks. There were e-mails and letters from cache, that show how tumultuous the relationship had become. She was a bathing suit designer for tommy hilfiger and victoria's secret. He was the trust fund baby of the composer who wrote "you light up my life." This morning, nicholas brooks is on trial for his own life. Accused of murdering his girlfriend, sylvie cache, in the sojo hotel in 2010. On tuesday, cache's friends testified shortly before she died, she e-mailed that brooks was bringing her down. Calling the 24-year-old a man-boy. One friend said that it was a really tumultuous relationship. Reporter: Cache's friends told jurors, when the 33-year-old designer discovered that brooks was hiring prostitutes, she wanted to break the relationship. When she tried to break things off, he choked and drowned her in the hotel room tub. Brooks has pled not guilty. His lawyers said cache took too many prescription pills that might and passed out in the tub. Prosecutors have painted brooks as a drug-using slacker. On friday, they suggested brooks had another reason to be angry. Presenting jurors with a five-page-long do-to list that cache allegedly made for him. No random drinking or drug use. If you can't do all these things, then this likely won't work. But brooks' lawyers say the couple was in love. He was out of the room having drinks with people he met at the hotel, when hotel workers discovered cache dead in the tub. And sylvie's family said in a statement, while we're agonizing the prosecution of her killer, we're determined to see that justice is done. And that sylvie's spirit and passion for life live on forever. We're going to bring in dan abrams for more on this. Dan, what are the key points in the prosecution's favor? In addition to what you heard amy talking about, which were letters she wrote, he was there. He checked in with her. This is the middle of the night. This is not an easy place to get into. This hotel/club. Random people don't walk around there. He asked a detective when they initially arrived how much time he could serve. If convicted of this. A witness heard an argument in their room. I mean, all of the evidence seems to point towards him. And yet, the defense is, she overdosed on drugs and as a result, she passed out in the tub. On top of all this, the medical examiner's report -- becomes absolutely crucial, right? The medical examiner says strangulation. If you believe the medical examiner, how do you not find a guilty verdict? If the medical examiner is right this is was strangulation, he's in big trouble. That's why the m.E.'S testimony, cross-examination of the m.E., the conclusions that are drawn here are going to be crucial. An investigator found it curious that she had on a sweater in the tub. And her family said she wasn't known for bathing or showering than taking a bath. Prosecutors are going to point to that as evidence they were in the middle of the fight. Or the defense could say, she was in the process of undressing when she passed out. The defense has a lot of explaining to do. They don't have a burden here. But all of the evidence points towards this. It's going to be interesting to see how they defend this case. Dan, thank you very much, as

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